This invention relates to plier tools and more particularly to a novel and improved tool for preparation of a coaxial cable to form a connection.
Plier tools especially suited for preparation of insulated electrical conductors for connection are now well known. Such tools are often referred to as xe2x80x9cwire strippersxe2x80x9d, although they typically include structure for crimping connectors into electrical contact with such conductors.
Coaxial cables are now widely used for cable television and other applications. Such a cable includes a central, axially disposed conductor surrounded by a coaxially disposed shield. The shield and conductor are separated by insulating material and further insulation surrounds the shield. The shield is typically an elongated braided wire tube.
When a coaxial cable is to be connected, it is necessary to strip both layers of insulation and a portion of the shield from around the central axial conductor. A further piece of the external or shield insulation is removed from around the shield to expose an end part of the shield. The reason for exposing the end part of the shield is to enable it to be grounded.
Once the insulation has been stripped from both the conductor and the shield, a suitable connector is secured to the conductor and the shield. Typically, the connector is connected to the conductor by crimping a metal sleeve forming a part of the connector into electrically conductive relationship with the conductor. Usually the connector is also in electrically conductive relationship with the shield in order to ground the shield.
Existing tools for cutting and stripping coaxial cable and securing appropriate connectors to them, have exhibited a number of shortcomings. As a first step in preparing a cable for use, a cable piece of desired length is cut from a supply which is typically a coil. Thus, an end piece of a cable is cut off in a manner which provides a good clean starting condition. Prior tools, when new, have been effective to perform such preparatory trimming, but with currently available cable, the blades for such end trimming quickly become nicked. They become nicked because coaxial cable manufacturers, in order to reduce costs, utilize copper coated steel conductors rather than solid copper. The result is greatly shortened useful life of the tools.
After an end of a cable has been cut to provide a clean starting condition, small end parts of both layers of insulation and the shield are removed. Thereafter a further small end part of the remaining shield insulation is cut and stripped to expose an end section of the shield.
With coaxial cable stripping tools, such cutting and stripping has heretofore been performed with cutters having coacting blades that effect shear cuts. A tool effecting such shearing is not fully satisfactory because it tends to cock when effecting a cut for stripping. Cocking results in a cut which is not normal to the axis of the cable.
Expressed another way if a prior stripping tool and the work piece are held rigidly as a shear cut of insulation around the wire or a shear cut of insulation around the coaxial shield is performed, the respective outer surfaces of the blades flare from their cutting edges outwardly so that. These flared outer surfaces effect a camming action against the insulating material which causes a cable to bend as the shearing action occurs. More importantly, as a stripping action occurs a leading tapered surface acting against the insulation being stripped applies a force which has components which has both axial of the cable and normal to it This force tends to apply a bending moment to the cable and more importantly to result in a scraping force against the cable shield or wire depending on which layer is being stripped. Considerable damage can be done by the blade, due to this bending moment, resulting in a scraping the coaxial shield or the cable central conductor as the case may be. In addition there is a tendency for the tool to strip improperly so that braids in the coaxial cable, for example, are pulled with the insulation. In short, shear action stripping tools do not work at all well on coaxial cable.
A further shortcoming is, because of tolerances in both the cable and the stripping tool, even the most skilled technician is apt to find that either the cutter did not fully shear insulation to be stripped, or that, where stripping is of insulation around the shield, the shield is hit by the cutters and damaged.
Accordingly, it would be desirable to provide a novel and improved coaxial cable preparation tool which overcomes the described shortcomings and others.
A plier tool made in accordance with the present invention has a pair of pivotally connected levers. Each lever includes jaw, boss and handle portions with the jaw and handle portions on opposite sides of the boss portion and the pivot. The jaw portions include connector crimping recesses for crimping standard size connectors onto coaxial cable conductors.
A pair of coacting cable shearing blades are positioned in the boss portions between the handle portions and the pivot and near the pivot. Each of these blades is unique in that it is comprised of a pair of blade sections that are connected at a juncture and that are at an obtuse angle with respect to one another. When the levers are moved from an open to a closed position to effect a cable trimming operation, these blade sections cam the central conductor to the juncture so that nicking caused by a copper clad steel conductors is confined to the junctures. This confining of the nicking assures good long blade life for cutting all of the cable other than the central conductor.
Each lever has a stripping section. Each stripping section includes a semicircular blade part and straight blade sections extending from either side of the semicircular part. On closing on a coaxial cable, the straight sections cut through surrounding insulation and the shield as do the semicircular parts until the straight parts abut and the semicircular parts define a circle surrounding the axial conductor. After the tool has reached its closed position, the cable and tool are relatively moved axially to strip the severed end parts of shield and insulation from the conductor.
Two pairs of sheath insulation cutters are provided to accommodate two standard sizes of coaxial cable. Each of the sheath insulation cutters includes a V-shaped section such that when the handles are in the closed position, the V-shaped sections of a pair define a diamond shaped opening.
The sheath insulation cutter pairs are disposed on opposite sides of the semicircular parts such that the straight sections extend from the semicircular parts to the sheath cutters. Further straight sections are on opposite sides of the sheath stripping sections such that the straight sections cooperate in the sheath stripping. The straight sections are in abutment when the tool is in the closed position such that cutting is effected by a nipping, as distinguished from a shearing action.
In stripping sheath insulation from a sheath, a cable to be stripped is inserted into a space between the appropriate one of the pairs of sheath cutters. The tool is closed until the V-shaped blades establish four points of contact with sheath insulation. The four points are disposed in an imaginary plane normal to the axis of the cable. As the handles are further closed, the V-shaped blades cut into the sheath insulation until they substantially contact the sheath at four spaced points. The tool and cable are then relatively rotated to sever the insulation fully and circumferentially. Typically, the relative rotation is accomplished either by spinning the tool around the cable or oscillating the tool until a full cut normal to the axis of the cable is accomplished. The cable and tool are then relatively moved axially to strip a cut part of sheath insulation from the cable. The cable is now in condition for crimp connection of a suitable connector.
The nipping cutting action for preparing the cable for both stripping the insulation and shield from the axial wire and stripping the shield insulation totally overcomes the problem with the prior art shearing tools. The problems are overcome because forces applied during this cutting action are circumferentially uniform and normal to the axis of the cable being stripped and the stripping action applies forces circumferentially and axially total avoiding the camming and bending action of prior shearing type tools. Since the camming or bending action is avoided stripping is clean without damaged to either the coaxial shield or the axial conductor.
Accordingly, the objects of the invention are to provide a novel and improved cable preparation tool and a method of preparing a cable for use.